Oven floor

[colinm]

I have designed a brick built oven that I am in the process of preparing the materials for and I wondered if anyone has any experience of casting the floor of the oven rather than using fire bricks? I haven't been able to find out much about it and there's probably a good reason for that, I wondered if a one piece base would be liable to cracking.

I am struggling to find any decent size fire brick tiles to minimise joins (I don't want to use lots of 230mm x 114mm fire bricks), although I have found some 600x300x76mm ones, so my options are casting a 75mm base on top of the calcium silicate or using the 76mm firebricks.

Any views?

[david s]

A one piece casting will definitely crack. Castable refractory is designed to be fired to service temperature in a very slow and controlled manner. This is not possible using wood as fuel. The temperature jumps up and down way too much especially with the fire sitting on top of the floor. In the 500-650 C range there are complex chemical changes that basically turn the material into the same as a fire brick. Below those temperatures the stuff just relies on the chemical bond of the calcium aluminate cement. The larger the casting the greater the tendency to crack because of uneven thermal expansion. This is why most oven floors have smaller cast units (bricks) that are laid loose. To allow for each to expand at their own rate. Building a fire in the centre heats those bricks up way faster than those at the perimeter. An oven dome is not subjected to such extreme heat changes and unsintered castable refractory does an adequate job, you can even get away with home brew as a castable there, but a floor is more problematic.